This invention relates to a thin film magnetic head for use in a magnetic disk apparatus and to a production method of the thin film magnetic head. More particularly, the invention relates to a thin film magnetic head having a small track width suitable for high-density recording and to a production method thereof.
Development of a thin film magnetic head excellent in recording/reading characteristics has strongly been required in recent years with improvement in a recording density of magnetic disk apparatuses and with improvement in performance of recording media. Heads using an MR (magnetoresistive effect) element or a GMR (giant magnetoresistive effect) element capable of acquiring a high reading output have been used at present as reading heads. A TMR (tunnel magnetoresistive) element capable of acquiring a higher reading sensitive has also been developed. On the other hand, an inductive thin film recording head of the prior art that utilizes electromagnetic induction has been used, and a read/write type thin film magnetic head having these reading head and recording head formed integrally with each other has been used.
To improve the recording characteristics of the thin film magnetic head, a strong and sharp recording magnetic field must be generated for sufficiently recording data to a recording medium having high coercive force. However, because a track width decreases with the improvement in a track density, magnetic saturation develops at a magnetic pole front end part of the thin film magnetic head and a recording magnetic field drops. Improvement in processing accuracy of a smaller track width has also been required to cope with the improvement of the track density.
JP-A-2000-276707 proposes a method for improving processing accuracy of a small track width that separates an upper magnetic pole to an upper magnetic pole front end layer and an upper magnetic pole top layer. As shown in FIG. 3, according to this method, a lower magnetic shield 2 made of a soft magnetic material is arranged on a substrate 1 made of a non-magnetic material to improve reading resolution and to eliminate influences of an external magnetic field, a reading gap 3 made of a non-magnetic insulating material is arranged on the lower magnetic shield 2, and a reading element comprising an MR or GMR element is arranged in the reading gap 3. A lower magnetic pole 5 made of a soft magnetic material and serving also as an upper magnetic shield is disposed on the reading element 4. A depth-defining non-magnetic layer 7 for defining a gap depth is arranged on the recording gap layer 6, and an upper magnetic pole front end layer 8 and an upper magnetic pole rear end layer 9 are further disposed on the recording gap layer 6. Gaps among these layers are filled with a non-magnetic insulating layer 10 and are planarized. A coil insulating layer 11 is disposed on the surface so planarized and a lower coil 12 and an upper coil 12xe2x80x2 are arranged inside the coil insulating layer. The coil is a single-layered coil in some cases. After an upper magnetic pole top layer 13 is disposed, the head is protected as a whole by a protective layer 14. The coils 12 and 12xe2x80x2 are so constituted as to encompass a rear end portion 16 of the upper magnetic pole top layer. When a reading current is applied to the coils 12 and 12xe2x80x2, a magnetic flux is induced in the upper magnetic pole top layer 13, the upper magnetic pole rear end layer 9 and the lower magnetic pole 5, and a signal is recorded to a recording medium 17 running in a spaced-apart relation by a very small distance from an air bearing surface 15 through a recording magnetic field generated from a front end of the recording gap. The magnetic flux concentrates on positions in the proximity of the recording gap from the lower magnetic pole and the upper magnetic pole front end layer. Consequently, a high recording magnetic field develops. A contact length of the upper magnetic pole front end layer 8 with the recording gap layer 6 is called a xe2x80x9cgap depth Gdxe2x80x9d. The magnetic flux concentrates much more on the magnetic pole front end when the gap depth Gd is smaller, so that the recording magnetic field increases.
When the upper magnetic pole front end layer 8 is formed, a photo resist is applied to the depth defining non-magnetic layer 7 and to the recording gap layer 6. The photo resist is exposed and developed through a mask having a predetermined shape of the upper magnetic pole front end layer. A portion of the photo resist that is to serve as the shape of the upper magnetic pole front end layer is then removed, and a high saturation flux density material to serve as the upper magnetic pole front end layer is formed at the removed portion in accordance with a plating method. In the thin film magnetic head according to the prior art, the photo resist for forming the upper magnetic pole front end layer 8 is formed on the slope of the depth defining non-magnetic layer 7. Therefore, when the photo resist is exposed, the shape of the upper magnetic pole front end layer cannot be formed with high accuracy due to reflection of light from the slope of the depth defining non-magnetic layer and due to insufficiency of the depth of focus. This problem becomes particularly serious when a narrow track width of the upper magnetic pole front end layer is formed.
To solve this problem, a method shown in FIG. 4 has been proposed. In this method, a lower magnetic pole front end layer 19 and a lower magnetic pole rear end layer 20 are arranged on the lower magnetic pole main layer 18, and the gaps between them is filled with a lower non-magnetic insulating layer 21 and is planarized. A recording gap layer 6 is formed. A resist frame is formed on this planarized surface and the upper magnetic pole front end layer 8 is then formed. In this way, the small track width can be formed with a high level of accuracy. However, according to this method, too, the lower magnetic pole front end layer 19 is processed by means such as ion milling with the front end portion of the upper magnetic pole front end layer 8 as a mask, and a projection portion of the lower magnetic pole front end layer 19 called a xe2x80x9ctrimming partxe2x80x9d is formed. At this time, the width of the upper magnetic pole front end layer 8 to serve as the track width decreases as a result of ion milling. Therefore, a problem yet remains unsolved in that accuracy of the track width cannot be sufficiently improved due to the limit of processing accuracy of ion milling even when accuracy of the track width formed by the frame plating method becomes high because the final track width is formed by processing such as ion milling.
Therefore, JP-A-11-7609 describes a method that forms the projection part of the lower magnetic pole without executing the trimming process by ion milling. This method forms the projection part of the lower magnetic pole, the recording gap layer and the upper magnetic pole front end layer inside a resist frame having the same shape in accordance with a plating method. In this case, only frame plating is used without conducting ion milling to form the track width, and the frame is formed on the planar surface of the lower magnetic pole 5 as shown in FIG. 5. Therefore, this method can acquire high track width accuracy. However, since the length of the lower magnetic pole projection layer 24 is equal to that of the upper magnetic pole front end layer 8, the contact length Lc cannot be sufficiently secured between the upper magnetic pole top layer 13 and the upper magnetic pole front end layer 8 when the gap depth is reduced. In this case, the recording magnetic field does not become high. When the contact length is increased, the gap depth becomes great, too. Consequently, the recording magnetic field does not become high, either. On the other hand, the recording magnetic field intensity required for the recording head has becomes higher and higher with the increase of the recording density, and a demand for a recording head that has a small track width and yet generates such a high recording magnetic field intensity has become higher and higher.
It is an object of the invention to provide a thin film magnetic head that can generate a high recording magnetic field even when a track width of a recording head decreases.
To accomplish a high recording magnetic field at a small track, a thin film magnetic head according to the invention includes a lower magnetic pole front end layer on a lower magnetic pole main layer, and a lower magnetic pole projection layer, a recording gap layer and an upper magnetic pole front end layer each having substantially the same planar shape are formed on this lower magnetic pole front end layer. The length of the lower magnetic pole projection layer, the recording gap layer and the upper magnetic pole front end layer from the air bearing surface to the head back direction is greater than the length of the lower magnetic pole front end layer. The thickness of the lower magnetic pole projection layer is smaller than the thickness of the lower magnetic pole front end layer. Since the thickness of the lower magnetic pole projection layer is relatively small, the lower magnetic pole projection layer in the proximity of the lower end portion of the lower magnetic pole front end layer gets into magnetic saturation and the leakage flux from the rear portion of the lower magnetic pole projection layer to the lower magnetic pole front end portion is restricted. Therefore, the gap depth is substantially defined by the rear end portion of the lower magnetic pole front end layer. On the other hand, since the upper magnetic pole front end layer is longer than the lower magnetic pole front end layer to serve as the gap depth, the contact length with the upper magnetic pole top layer can be sufficiently secured. As a result, a high recording magnetic field can be acquired.
Because the lower magnetic pole front end layer and the lower magnetic pole projection layer can be formed of mutually different materials, it becomes possible to constitute the lower magnetic pole front end layer by a magnetic material having high corrosion resistance and the lower magnetic pole projection layer by a magnetic material having high saturation magnetic flux density. In this way, a recording head satisfying both high corrosion resistance and high recording magnetic field can be accomplished.
It is another object of the invention to provide a method of producing a thin film magnetic head capable of accomplishing a high-precision track width.
In the invention, a lower magnetic pole projection layer, a recording gap layer and an upper magnetic pole front end layer each having substantially the same planar shape are formed. These layers are formed by a plating method inside the same resist frame formed on a planar surface constituted by a lower magnetic pole front end layer and a lower non-magnetic insulating layer. Since the resist frame is formed on the planar surface, scattering and irregular reflection of exposure light are less and eventually, a resist frame having high accuracy can be formed. Furthermore, since the lower magnetic pole projection layer, the recording gap layer and the upper magnetic pole front end layer are formed inside the same resist frame, the projection portion of the lower magnetic pole can be formed without employing ion milling and a narrow track width having extremely high accuracy can be formed.